This invention relates to an electromagnetically operated rotary servovalve, particularly suitable for operating hydraulic actuators, such as the actuators which control the hydraulic active suspensions of a vehicle.
For the running safety of a vehicle it is known to be important to be able to rapidly adapt the geometrical, elastic and damping characteristics of vehicle suspensions to the particular road situation in which the vehicle finds itself at any given time. For this purpose, active suspensions have been designed incorporating hydraulic actuators. By controlling the feed flow to such actuators using suitable electromagnetically operated servovalves controlled by appropriate central electronic units, the suspension characteristics, such as the rigidity, amplitude, height of the vehicle from the roadway etc. can be influenced. Currently used servovalves, whether offering discrete or on-off flow control or whether operating on a continuous control basis, are all of the sliding spool type. The spool position controls the feed flow to the actuators and is regulated either by a hydraulic low-pressure secondary control circuit controlled by a device of blade/nozzle type itself controlled by electromagnets, or directly by linear electromagnetic actuators which attract the opposing ends of the spool. Directly controlled servovalves absorb a large quantity of electric current in operating the electromagnetic actuators, are bulky and in particular have an unsatisfactory response speed, so making it impossible to adapt the suspension characteristics to the vehicle running situation in useful time. Indirectly controlled magneto-hydraulic servovalves are rapid and accurate but are also bulky, are of generally complicated construction and are of high cost.